This invention relates to a unique fuel and more particularly to a fuel comprising a mixture of finely ground coal, water, a wetting/dispersing agent and a suspending agent.
It has long been known that the present supply of oil is rapidly being depleted. Because of the possible future world shortage of oil and the current price increases in petroleum products, the use of oil as a source of energy has become very expensive, while as indicated above, the supply has an uncertain future. The prior art cognizant of such problems attempted to alleviate the demand for fuel oils by substituting other types of fossil fuels. The abundance of coal and its ready accessibility suggested a direct substitution of coal for oil in many applications. Hence considerable effort has been expended in formulating mixtures of oil and finely ground coal in the ratio of 50 percent oil/50 percent coal to 70 percent oil/30 percent coal.
Examples of typical formulations and techniques are depicted in U.S. Pat. No. 4,147,519 entitled Coal Suspensions in Organic Liquids issued on Apr. 3, 1979 to Edgar W. Sawyer, Jr. the inventor herein and assigned to this assignee.
This Patent describes coal dust powder suspended in fuel oil and stabilized against sedimentation by an additive that makes the mixtures viscous under conditions of low shear while exhibiting low viscosity under high shear conditions to facilitate pumping through long range pipelines by the combination of a suitable surfactant with a gelling grade clay as a suspending agent.
U.S. Pat. No. 4,251,230 entitled Coal Suspensions in Organic Liquids issued on Feb. 17, 1981 to E. W. Sawyer, Jr. describes a suspension of coal dust powder in fuel oil, which suspensions are also stabilized using a gelling grade clay suspending agent.
Other Patents are U.S. Pat. No. 4,062,694 entitled Stable Particulate Suspensions which issued on Dec. 13, 1977 to E. W. Sawyer, Jr. and describes the use of attapulgite clay as a suspending agent for coal dust in flammable liquid hydrocarbons to formulate fuels which facilitate the removal of fly ash from the fuel assembly after burning. As indicated such prior art as well as other Patents, such as U.S. Pat. No. 2,397,859 entitled Liquid Fuel and Method of Producing the Same issued on Apr. 2, 1946 to A. B. Hersberger, et al. attempt to substitute coal for a portion of the oil and provide a composite fuel.
U.S. Pat. No. 4,062,694 also describes coal dust-water slurries that exhibit good rheological characteristics and are useful for transporting and storing coal at a 60% concentration. The slurry is formed using coal, a wetting/dispersing agent for the coal and 1% to 3% gelling grade clay. The 60% coal concentration did not provide sufficient Btu's for the slurry to be considered a satisfactory fuel. The high water content had to be evaporated and that consumed too much of the heat content. The slurry also contributed to another problem, that being ash content. The 1 to 3% clay level contributed significantly to an unacceptable ash level.
Certain of the mixtures depicted in the prior art have been burnt successfully in certain types of furnaces.
The problem with the oil-coal mixtures is that they still contain fuel oil and do so in considerable percentages as between 50 to 70 percent oil.
It is of course understood that the ideal situation is to completely eliminate oil from the composite fuel. Many present installations are designed for powdered coal combustion and have, due to environmental considerations, been retrofitted to burn oil. However, many of the previously retrofitted installations no longer have the auxiliary room and facilities to receive, store and grind coal and therefore changing back to coal or powdered coal combustion is not possible.
It is therefore an object of the present invention to provide a fuel composition which will allow the use of powdered coal as a fuel in the above-mentioned isolated facilities, thus resulting in substantial savings in cost.
Another object is to provide an improved fuel composition employing powdered coal without any fuel oil to provide an efficient stable and economical alternate fuel composition, as well as economical processes for making the composition.